n your formal proofs in this question, you can only use the $11$ rules of Formal Deduction,

and the following proved theorems:

$$ Membership $($ in $)$

$$ Negation introduction $(+)$

$$ Double$-$negation $()$

$$ Transitivity $($Tr$.)$

$$ Hypothetical Syllogism $($Hyp$.$ Syll$.)$

$$ Disjunctive Syllogism $($Disj$.$ Syll$.)$

$$ Contrapositive $($Contr$.)$

$$ Replaceability of Equivalent Formulas $($Repl$.).$

Provide Formal Deduction proofs for the following theorems. Do not use Soundness or

Completeness.

$($c$)($C $$ B$),$ D $->($A $$ B$),$ A $->$ C $$D$.$